The rise of the Mountains of the Moon is perhaps the best-documented geologic event on Westeros, and is directly responsible for the tremendous wealth of the House Lannister. Similar to the Black Mountains to the north, the Mountains of the Moon are jagged, rocky, and snow capped. Based on morphology alone, we cannot rule out that the Black Orogeny and the Moon Orogeny occurred simultaneously. However, analysis of the most-likely faulting geometry reveals that the Mountains of the Moon exist to the south of a microplate (yes, microplates exist on Earth too). Based on this geometry, it is more likely that the Moon Orogeny occurred slightly earlier than the Black Orogeny (similar to the microplate tectonics responsible for the Mariana Trench and volcanic island arc of Japan). Knowing that the Black Mountains are 60-80 million years old, we therefore surmise that the Mountains of the Moon are 80-100 million years old, comparable to the Canadian Rocky Mountains in North America. The Moon Orogeny is more complex than the Black Orogeny, and we propose that the Mountains of the Moon formed in two stages: 1) early subduction of the microplate beneath southern Westeros, and 2) later continental collision between northern and southern Westeros.
The more recent continental collision between northern and southern Westeros is evident in the width of the Mountains of the Moon, far wider than the Black Mountains, and nearly twice the width of the Himalaya on Earth. While most mountain ranges on Earth formed as a result of subduction (think: Rocky Mountains, Alps, and Andes), the much larger and wider mountains of the Himalaya formed as a result of two continents (India and Asia) colliding with little to no subduction. This is the most striking evidence of a collision between northern and southern Westeros. Yet these mountains are also home to Casterly Rock and the gold deposits from which the House Lannister has so benefited. Gold is typically deposited on the ocean floor near mid-ocean vents. The gold mixed with the basalt (extrusive igneous rock) until it reached a subduction zone. As the oceanic crust that previously separated northern and southern Westeros subducted beneath the southern part of Westeros, layers of ocean rock were scrapped off (like a bulldozer), accreted onto the continent, and uplifted. The heat and pressure of subduction dissolved the gold, which then intruded into the overlying rock and solidified within quartz veins (this is where the gold from the California Gold Rush came from). The presence of the Lannister gold (and silver found at Silverhill to the south) supports the notion that subduction tectonics played an equally important early role in the Moon Orogeny.
The final piece of evidence that northern and southern Westeros were previously separate continents is the Iron Islands. On Earth, iron ore is most widely extracted from rocks known as banded-iron formations (more on these later). These rocks formed in shallow oceans. During the initial subduction phase, the ocean floor that wasn’t directly scraped off onto southern Westeros (as Casterly Rock had) was uplifted, pushing the banded iron formations that make the Iron Islands to the surface. Millions of years of exposure, erosion, and weathering have left behind only the strongest of rocks. But their very presence owes to uplift caused by the subduction of the microplate.